1. Field of the Invention
Embodiments of the invention generally relate to methods and apparatus for determining at least one flow velocity/rate for one or more phases within a multiphase fluid flow.
2. Description of the Related Art
In the petroleum industry, as in many other industries, ability to monitor flow of certain fluids in process pipes in real time offers considerable value. Oil and/or gas well operators periodically measure water/oil/gas flow rates within an overall production flow stream containing a mixture of these three phases. This information aids in improving well production, allocating royalties, properly inhibiting corrosion based on the amount of water and generally determining the well's performance.
While some techniques enable measuring flow rates within two phase mixtures, difficulty arises in determining individual volumetric fractions and flow rates in three phase mixtures. Separators can be used to separate out one or more phases from the flow stream, but they introduce additional equipment and costs. Other costly and time consuming procedures entail manual sampling of the mixture to obtain information regarding the individual volumetric fractions. On the other hand, flowmetering devices can be complex and can restrict flow creating significant pressure loss, such as when venturi based measurements are required.
In many instances, multiphase flowmeters utilize a method to measure a flow rate of the entire flow stream and another process to measure volume fractions of oil, water and gas. This measured information when applied to flow models enables estimation of each of the individual phase flow rates. However, the flow models make assumptions regarding the flow characteristics such as by modeling with the flow model the slippage velocity between the liquid and gas phases. Therefore, the flow models cannot completely account for uniqueness of each particular fluid flow. In other words, application of these flow models with measured total flow and volume fractions does not permit direct measurement of actual phase velocities and flow rates independently.
Therefore, there exists a need for improved methods and apparatus that enable determining at least one flow velocity for one or more phases within a multiphase fluid flow and hence flow rate for the one or more phases.